The invention relates to a unit for delivering fuel from a supply tank to an internal combustion engine. In one such supply unit, known from U.S. Pat. No. 4,592,311, an electric drive motor drives the impeller of a pump, embodied as a peripheral pump, to rotate. The disklike impeller, revolving in a cylindrical pump chamber, has a ring of blades, spaced apart from one another circumferentially of the impeller and ending at its two axially oriented end faces. In the chamber walls that define the pump chamber on the face ends, supply conduits are disposed via a split ring, at the level of the axially pointing blade ends, around the pivot axis of the impeller; they lead from an inlet opening to an outlet opening of the pump chamber, and the inlet opening is disposed in a first chamber wall, formed by an intake cap that closes off the pump, and the outlet opening is disposed in a second chamber wall, formed by an intermediate cap toward the drive motor. During operation of the known feed pump, the fuel is aspirated into the pump chamber via the inlet opening and pumped onward to the outlet opening via the supply conduit, with an increase in fuel pressure taking place as a result of the exchange of impetus between the fuel accelerated in the impeller and the fuel revolving in the supply conduit; from the outlet opening, the fuel is carried on to the engine that is to be supplied.
To allow unthrottled inflow of the requisite quantity of fuel into the supply conduit even if the proportion of gas bubbles in the aspirated fuel, in particular the hot fuel, is high, the supply conduit of the known fuel feed pump has an enlarged cross section at its end that covers the inlet opening; adjoining the inlet opening, this decreases via a step to a smaller cross section, which then extends constant over an angular range of approximately 70.degree.. Adjoining this constant range, the cross section of the supply conduit decreases once again across a second step to a smaller value, which then again remains constant onward to the region of the outlet opening. For dissipating the gas bubbles from the supply conduit, a degassing bore communicating with a low-pressure chamber is provided in the first constant region of the supply conduit and opens into it a short distance from the second step.
However, the known delivery unit has the disadvantage that the gas bubbles aspirated into the supply conduit cannot be broken down completely or completely dissipated via the degassing bore, and hence they have a deleterious effect on the delivery characteristic, particularly when the fuel is hot, and also decrease pump efficiency.